The present invention concerns an arrangement for an internal combustion engine comprising a throttle valve in an intake pipe of the engine and a speed control regulator connected to the throttle valve. The regulator includes an actual value and a desired value signal generator as well as a throttle adjusting element, controlled as a function of the difference between actual and desired values, connected to actuate the throttle valve during non-idling operation of the engine. Means are provided for moving the throttle valve into its idling position when the supply voltage to the regulator is disconnected.
An arrangement of above-described type, whereby the throttle adjusting element is connected with the throttle valve only during non-idling operation of the engine, is disclosed in the West German Pat. No. 2,120,510. In this case an electromagnetic coupling is provided between the shaft of an adjusting motor which constitutes the throttle adjusting element, on the one hand, and the throttle valve spindle, on the other. The electromagnetic coupling is actuated by an exciter circuit having a thermal switch which closes the circuit only when the internal combustion engine reaches a given minimum temperature. A return spring acting on the throttle valve spindle serves to move the throttle valve into its idling position when the voltage supply to the speed control regulator is disconnected for any reason. This return spring also maintains the throttle valve in its idling position whenever the aforementioned electromagnetic coupling is not excited. Thus, when the engine is started, the speed control regulator operates--i.e., produces a control signal-- but this signal is not transmitted to the throttle valve due to the non-excited state of the electromagnetic coupling.
Accordingly, an advantage of this known arrangement is that, in case of failure of the supply voltage of the speed control regulator, the throttle valve is moved into its idling position and not to a position in which the engine speed assumes undesirably high values. On the other hand, this known arrangement has the disadvantages that () the adjusting motor operates continuously prior to attainment of the prescribed engine temperature and (2) the other control devices of the internal combustion engine, such as mechanisms for ease of starting, must act directly on the throttle valve spindle. This latter condition leads to complex arrangements which are subject to the effects of inertia. Moreover, the moment at which the speed control regulator commences to control the throttle valve is not precisely determined in the prior art system because it is ultimately dependent upon the time at which the thermal switch closes in the exciter circuit of the electromagnetic coupling.
It is a principal object of the present invention to provide apparatus of the above-described type which avoids these various disadvantages.